Answer: Python Puzzler #864

The answer is B. The program prints:

##
##
##

Why?

The outer loop runs 3 times (one per row). Inside it, the inner loop adds 2 symbols to line. So you get 3 rows of 2.

Trace table

A trace table follows the program step by step. Here’s this one:

row	line printed
0	##
1	##
2	##

The code again

for row in range(3):
    line = ""
    for col in range(2):
        line = line + "#"
    print(line)